What is ply?
Ply refers to the number of individual yarns used as a strand. Single ply fabric is woven from one, individual yarn; 2-ply fabric is made from yarns that are twisted together and then woven. If 2-ply yarn is used, the finished construction will have twice the thread count of the same construction made from single ply yarn. 2-ply yarn must be made from a very high yarn size (like 100) or they will feel thick and heavy.